1. Field of the Invention
The present invention relates to a dielectric filter unit formed by disposing a plurality of resonators in a dielectric block. The invention also relates to a transmitting/receiving-sharing unit and a multiplexer, both of which are configured similar to the above dielectric filter unit.
2. Description of the Related Art
A typical example of a known dielectric filter unit having a plurality of filters formed in a single dielectric block is shown in FIG. 11. In FIG. 11, a dielectric block 1 has an external conductor 8 on the outer surfaces other than the top surface of the block 1. A plurality of through-holes 2, 3a, 3b, etc. for receiving internal conductors therein are provided on the top surface of the block 1. Further, electrodes, which are continuously extending from the exposed surface (top surface of FIG. 11), are formed to capacitively couple adjacent resonators. Moreover, an input/output electrode 7a is disposed between the adjacent internal-conductor through-holes 2 and 3a on the exposed surface of the block 1, thereby capacitively coupling the input/output electrode 7a and its adjacent internal conductors. In this example shown in FIG. 11, the internal-conductor through-hole 2 serves as a trap circuit, while the internal-conductor through-holes 3a, 3b, etc. function as a band-pass filer (BPF). Also, the input/output electrode 7a is shared between the trap circuit and the band-pass filter.
The above types of dielectric filter units used as an antenna sharing unit by forming a plurality of filters in a single dielectric block are disclosed, for example, in (1) PCT/US93/03693 WO93/24968 and (2) PCT/US95/01676 WO95/30250. The publication (1) discloses a dielectric filter unit, configured in a manner similar to the unit shown in FIG. 11, in which a common input/output electrode is provided each at the input/output portion between a trap circuit and a BPF and at the input/output portion between BPFs. The publication (2) discloses a dielectric filter unit in which an input/output electrode is coupled to a resonator interposed between two BPFs.
The above known types of dielectric filter units however present the following problems. In the filter units of the types shown in FIG. 11 and disclosed in the publication (1), since the two filters having the common input/output electrode are located in proximity with each other across the electrode, unwanted coupling is caused between the filters, thereby failing to obtain desired characteristics. If the distance between the two adjacent filters is increased to overcome the above drawback, the overall filter unit is disadvantageously enlarged. Further, in the filter unit of the type disclosed in the publication (2), since a resonator is shared between two filters, an external coupling circuit is also shared therebetween, thereby making the design of the filter unit complicated and also decreasing the design flexibility.